Tom Volk's Fungus of the Month for March 2000

This month's fungus is Entomophthora muscae, a fungus that infects houseflies.

This month's fungus (and its host) is actually still stuck to the back window of my house. I found it there a couple of months ago when I spotted this large housefly with a halo of spores surrounding it. Fortunately I knew what it was and took pictures to use for the fungus of the month during the winter, when there aren't too many fungi out in nature to look at. This particular fungus is called Entomophthora muscae (ent-uh-MOF-thor-uh MUSK-eye). Entomo- means insect, -phthora means destroyer, so this is the "insect destroyer." Muscae means "of the fly." The fungus belongs to the Zygomycota, but rarely forms zygospores. It is a member of an order of mostly entomoparasitic fungi called the Entomophthorales. I'll have more to say about these other insect destroyers later. I've also seen this called Entomophthora coronata, which means "insect destroyer with a corona," referring to the corona (like during a solar or lunar eclipse) of spores that is formed when the fungus sporulates around the fly. Apparently this is an incorrect name. (Thanks to Kathie Hodge of Cornell University for this clarification).
So how did the fly get stuck to my window? This particular fungus produces abundant spores, and the fly must have had the misfortune of having one of the spores land on it a few days previous to its untimely demise. The spore germinated and penetrated the exoskeleton of the fly, or grew in through one of many cracks in the fly's "armor." The first thing the fungus does, according to some reports, is grow up into the brain of the fly, in order to control its activities. The mycelium of the fungus grows into a particular area of the brain that controls the crawling behavior of the fly, forcing the fly to land on a nearby surface and crawl up as high as possible. Eventually the hyphae of the fungus grow throughout the body of the fly, digesting its guts, and the fly dies. Small cracks open in the body of the fly and the Entomophthora produces sporangia, each with a single spore, in pads. Remember that most fungi want to get their spore bearing structures as high as possible, so that the spores will get caught in air currents more easily. Other fungi produce fruiting bodies to accomplish this but Entomophthora takes advantage of its relationship with the fly to get its spores as high as possible.

To the right and up you can see a longitudinal section of the abdomen of the fly filled with fungal hyphae and with three pads of sporangia bearing spores on the upper surface. To the left is a close-up of one of these pads of sporangia with their spores. The circular spores are forcibly shot off by the sporangia and are what you can see on the glass of my window in the first picture. Enormous numbers of spores are produced in the "hope" that a few of them will actually land on flies and continue the life cycle. This fungus is a fascinating find for any mycologist or student.

So what good could this be for us humans? Well if you're thinking, you're already ahead of me, and you're wondering whether Entomophthora could be used for biological control of these annoying insects. The answer is apparently yes, although there are some technical problems, such as the short lifespan of the spores. These biological controls would be far better to use than conventional insecticides, which are most broad spectrum, killing a wide variety of insects as well as being toxic to animals, including humans. Most of the bioinsecticides are specific to one species or at least a genus or family of insects, so they can target only the group the scientist want to eliminate. There are also species in the Entomophthorales that target species of other insects such as moths, aphids and grasshoppers. This is an area of active research, blending Entomology and Mycology very well.

I hope you enjoyed this month's fungus. Be on the lookout for flies and other insects stuck to your walls and windows with a halo of spores around them. They're actually quite common-- but not as common as we would like. Don't forget to shut the screen door on your way out --- you're letting flies in....

If you have anything to add, or if you have corrections or comments, please write to me at volk.thom@uwlax.edu